With known brushless direct-current motors, energizing the Stator windings is performed via an inverter. The permanently magnetized rotor follows the revolving field. In order to regulate to predetermined values, data are obtained from the drive, the inverter and/or the upstream voltage transformer and are processed in the control logic in connection with a speed value to be used to drive the motor, into signals controlling the inverter, so that the inverter is able to generate the required alternating voltage to be applied to the windings.
In order for the rotor to be able to follow a voltage curve at a predetermined speed in the best possible manner, a certain phase angle must exist between voltage and current, the voltage is ahead of the current, which requires a different angle depending on the load. If, in consideration of the load to be driven by the motor, adjustment is made strictly to this angle, then electronics must be configured for the high idle current resulting from the maximum load, requiring component expenditures.
From EP 2 133 991 B1, a centrifugal pump aggregate with an electric drive motor and a control device comprising a frequency converter for speed regulation is known. The control device is designed such that a weakening of the drive motor's field is generated in a predetermined control range, so that the drive motor's speed is increased.
U.S. Pat. No. 6,965,212 describes the operation of an electrical drive motor utilizing field weakening. Field weakening facilitates a minimizing of the voltage necessary to energize the motor at a specific speed.